Dual cure composite resins containing uretdione and usaturated sites

ABSTRACT

The present invention provides a dual-cure composition containing multifunctional polyols, uretidiones, peroxide curable monomers containing unsaturation and crosslinking agents. The dual-cure composition may be used to form a high modulus material useful as the matrix in a prepreg material and in composites. The present invention also relates to methods for the production of the dual-cure composition, prepreg materials comprising the dual-cure composition and a fibrous support, and composites made from the prepreg material.

BACKGROUND OF THE INVENTION

The present invention pertains generally to a dual-cure compositioncontaining uretidione groups and unsaturated sites. More specifically,the invention pertains to compositions containing multifunctionalpolyols, uretidiones, free radical curable monomers containingunsaturation and crosslinking agents which may be used to form a highmodulus material useful in composites and in the production of prepregs.

Fibers or fabrics pre-impregnated with polymer or resin matrices,“prepregs”, have become increasingly common in the composite industry asthey offer several major advantages. One of the biggest advantages is agreater ease of use. Prepregs arrive as solid preformed sheets which canbe stored prior to use in composite parts fabrication. Furthermore,methods of composite parts fabrication using hand layup in an openmolding process or infusion into closed molds requires the use of liquidresins, solvents and hardeners which can be time consuming, messy andinefficient. For example, in a hand layup process much of the materialis wasted in achieving a proper resin mix, and on the rollers, sprayersand other application equipment used to form the composite part.

Moreover, it is difficult to achieve high fiber or fabric content in acomposite part using hand layup methods, with an industry standard beingabout 40% fiber or fabric. The low fiber content and thus increasedresin content increases brittleness and diminishes the overallstructural properties of the final fabricated composite part. Prepregs,on the other hand, can provide a near perfect resin content which leadsto greatly improved strength properties and a higher volume capacity.Prepregs typically contain 65% or more fabric, leading to improved curetimes and increased strength. Furthermore, the optimal resin content ofprepregs leads to improved uniformity and repeatability of the finalcomposite part. Without the pitfalls of human lamination techniques,there are neither resin rich nor resin dry spots. Thickness is uniformand every part that comes out of the mold has a theoretical likelihoodof being identical.

Another advantage of prepregs is that they allow for the use of a widerrange of polymer or resin matrices. The accuracy of the machinery usedto produce prepregs enables the use of very tough and strong resinsystems that would be too high in viscosity to be impregnated by hand.

Today, prepregs find use in commercial aerospace, military/defense,general aviation, space/satellite, marine, sporting goods, automotive,civil engineering, wind energy and the transportation markets. The windenergy industry, for example, is one of the fastest growing consumers ofprepregs in the world as energy from wind power is currently thefastest-growing source of electricity production in the world.Contemporary wind turbines are fitted with three blades, each of whichcan reach 80 meters in length and weigh as much as 35 tons. These bladesare typically 70 to 75% E-glass by weight infused with epoxy orunsaturated polyester resins. In 2011, there were 23,640 new windturbines built globally. At the current growth rate, U.S. wind energydevelopers install two new wind farms per week, with tens to hundreds ofturbines per farm. As such, an area of intensive research anddevelopment has been the quality of the rotor blades that are produced,and less expensive production methods and materials.

It is known that prepregs can be produced from a number of differentsynthetic polymers or resins and various fibers or fabrics. Glass fibershave proved to be a particularly advantageous reinforcing material.Epoxy, vinyl ester, bismaleimide, cyanate ester, phenolic, polyimide,polyetheramide and polyester resins have been processed with glassfibers to create storable prepregs which can be formed by means ofheated presses and hardened to generate composite parts combining highstrength with rigidity. This process is, however, attended by severaldisadvantages which often depend on the matrix material selected.

One shortcoming in the abovementioned prepregs is that they have arelatively short shelf-life. Heat cures prepreg materials and storage atwarmer temperatures will reduce their shelf-life. Keeping the materialcooler, such as by freezing, may extend the shelf-life significantly butadds another set of problems. Prepregs stored at low temperatures needto be wrapped and sealed in polythene and must be fully thawed beforebreaking the polythene seal in order to avoid moisture contamination.Epoxy resins, for example, are able to absorb water easily, thus storageconditions and processing methods may be critical to obtaining a uniformcomposite part.

Another shortcoming is that relatively high heats must be applied to theprepreg material in a mold to cure the polymer or resin and form thefinal composite part. For each prepreg resin system there is a minimumcure temperature and a range of options for cure temperature andduration. The oven or autoclave, the laminate, and all tooling (molds)need to reach and maintain the given cure temperature throughout thespecified cure cycle. Frequently, the cure temperature exceeds thetemperature that the fiber materials and/or molding equipment canhandle. Bismaleimide resins, for example, are cured at 180° C. for threehours during which time the resin exhibits a low viscosity. A typicalcure cycle for cyanate ester resins includes temperatures as high as260° C. Many fibers and fabrics may not withstand such high curetemperatures and the low viscosity makes the molding processproblematic.

Additionally, if the resin material has a high exotherm, the heatgenerated within the prepreg may exceed the temperatures that the fibermaterials and/or molding equipment can withstand leading to a discoloredor scorched composite part. As such, polymer or resin matrices withlarge exotherms may only be used in thin layers to avoid excessive heatbuild-up. Certain epoxy resin matrix formulations, for example,demonstrate exotherms in excess of 300 μg which can lead to uncontrolledpolymerization and excessive heat formation.

An additional shortcoming is the use of solvents, reactive diluents andother toxic materials in certain polymer or resin matrices. For example,unsaturated polyester resins often require reactive diluents such asstyrene during the free radical initiated polymerization reaction(cure). Both solvents and reactive diluents have also traditionally beenused to lower the viscosity of matrix materials and thus provide forbetter fiber wet-out properties and improved ease of handling. Reactivediluents are known to lead to a very high crosslink density which canmake the final product extremely brittle and reduce its notched impactstrength. Solvents, on the other hand, complicate processing aselaborate measures must be taken to extract the solvent vapors and, inmany installations, explosion-proof processing equipment becomesnecessary.

Alternative polymer matrices include polyurethanes which use uretidionesas the crosslinking agents. Uretidiones are, in effect, self-blockedisocyanates that provide the desired urethane or allophanate linkageswhile offering a latent heat induced reactivity without the release oftoxic blocking agents. The prior art has recognized the advantagesassociated with this latent reactivity, but has for the most part failedto make practical application of this concept in prepreg matrixformulations which may be cured at lower temperatures.

By way of illustration, disclosures of the preparation of crosslinkablepolyurethane rubbers and elastomers which take advantage of the latentreactivity of the uretidione linkage can be found in U.S. Pat. Nos.3,099,642 and 3,248,370. The processes described in these referencesinvolve combining, at temperatures of less than 100° C., a relativelyhigh molecular weight (e.g., on the order of from 500 to 3,000 daltons)difunctional resin, a low molecular weight crosslinking reagent, and auretidione diisocyanate, or a mixture of a uretidione diisocyanate and amonomeric diisocyanate. The resulting, essentially thermoplastic,formulations contain an excess of isocyanate reactive groups, and theseformulations are finally cured to a crosslinked thermoset polymer bytreatment at temperatures in excess of 140° C.

U.S. Pat. No. 4,138,372 discloses a prepreg matrix material comprisingepoxy resins which are cured using the latent reactivity of theuretidione linkage. Dissociation of the uretidione ring to isocyanateswas found to take place at about 170° C. in the absence of catalysts,while catalysts such as tetraphenyl borate-amine complexes lowered thedissociation temperature to some extent. At the high temperatures usedin the aforementioned patents, however, the uretidione ring most oftendissociates to form free isocyanates.

Furthermore, because of the environmental and economic requirementsimposed on the matrix materials, i.e., that they should use as littleorganic solvent as possible or none at all, for adjusting the viscosity,there is a desire to use raw materials which are already of lowviscosity. Known for this purpose are polyisocyanates with anallophanate structure as are described in U.S. Pat. No. 6,392,001.

The formation of allophanate compounds by ring opening of uretidioneswith alcohols is known in principle as a crosslinking mechanism inpowder coating materials. Nevertheless, the reaction temperaturesrequired for this purpose, in the absence of catalysts, are too high(≧130° C.) for many prepreg applications. Catalysts such asorgano-metallic compounds have been found to lower the reactiontemperatures (<130° C.; cf. Proceedings of the International Waterborne,High-Solids, and Powder Coatings Symposium 2001, 28th, 405-419).

Historically, the direct reaction of uretidione rings with alcohols toform allophanates was first investigated for solventborne,isocyanate-free, 2K [2-component] polyurethane coating materials.Without catalysis, this reaction is of no technical importance due tothe low reaction rate (F. Schmitt, Angew. Makromol, Chem. (1989), 171,pp. 21-38). With appropriate catalysts, however, the crosslinkingreaction between hexamethylene diisocyanate (HDI)-based uretidionecuratives and olefinic unsaturated alcohols is reported to begin at<130° C. (U.S. Pat. No. 8,202,618). The use of uretidione groups ascuring agents in prepreg materials which cure from 100 to 160° C. hasalso been disclosed in U.S. Pat. Application 2012/0003890. The prepregsaccording to the invention use matrix materials which have Tg values of≧40° C. As such, the matrix materials are dry when applied to the fiber,and the prepreg material lacks any tack. In certain industries, aprepreg material with a certain amount of tackiness may aid in aligninglayers in a mold.

It was, therefore, an objective of the present invention to develop newsolvent-free, storable matrix compositions which may be hardened at lowtemperature to form composites which combine high impact strength anddimensional stability. An additional objective of the present inventionwas to develop new prepreg materials with low exotherms and low pre-cureglass transition temperatures, yet high post-cure glass transitiontemperatures that would be useful in the renewable energy market.

SUMMARY OF THE INVENTION

According to its major aspects, and briefly stated, the presentinvention includes a dual-cure composition which may be used as thematrix in a prepreg material, a prepreg material comprising thedual-cure composition and a fibrous support, and methods for producingthe dual-cure composition, the prepreg material comprising saiddual-cure composition, and composites made from the prepreg material.

The present invention relates to a dual-cure composition which cures at80-130° C. and has a heat of polymerization of less than 170 J/g,preferably less than 130 J/g, comprising:

a multifunctional diol or polyol, which may be a free radically reactivemonomer selected from the group consisting of a vinyl ether, an allylether, an acrylate, a methacrylate, a urethane acrylate, alone or in amixture, or may be a non-free radically reactive oligomer selected fromthe group consisting of an ether, an epoxy, an alkyd, a urethane, aloneor in a mixture;

a curing agent containing uretidione groups, which may consistessentially of a curing agent containing at least one aliphatic,cycloaliphatic or aromatic polyisocyanate selected from the groupconsisting of isophorone diisocyanate (IPDI), hexamethylene diisocyanatediisocyanatodicyclohexylmethane (H₁₂MDI), diphenylmethane4,4′-diisocyanate and diphenylmethane 2,4′-diisocyanate (MDI), and 2,4-and 2,6-toluene diisocyanate (TDI);

a low viscosity unsaturated reactive diluent, which may be a peroxidecurable monomer selected from the group consisting of a (meth)acrylate,a urethane (meth)acrylate, a polyester (meth)acrylate, a polyether(meth)acrylate, an allyl ether (meth)acrylate, an ester (meth)acrylate,an allophonate urethane (meth)acrylate, an epoxy (meth)acrylate, a vinylether, alone or in a mixture;

at least one reactively activatable catalyst, which may be (i) a lewisacid comprising at least one metallo-organic catalyst of the generalformula R_(n)MeX_(y) in which Me means a metal, R means an alkylresidue, X means a carboxylate residue, an alcoholate residue, or anacteylacetonate residue, n=0 or 2, and y=2 or 3, or (ii) atetralkylammonium salt and/or phosphonium salt with halogens, withhydroxides, with alcoholates or with organic or inorganic acid anions ascounter-ion;

a thermal crosslinking initiator, which may consist essentially of aperoxide or hydro-peroxide compound, or an initiator which can beactivated by actinic radiation;

optionally (G) an acid scavenger such as an epoxide; and

optionally (H) an acrylate co-catalyst.

The present invention also relates to a process for the production of adual-cure composite comprising:

homogenizing a pre-polymer composition comprising components (A), (B),(C), optionally (G), and optionally (H) as listed above;

heating the pre-polymer composition to a temperature above the Tg ofcomponent (B);

cooling the heated pre-polymer composition to a temperature of less than110° C.;

mixing the cooled pre-polymer composition with a dual-cure catalystcomposition to form a dual-cure composition, the catalyst compositioncomprising components (D) and (E) as listed above; and

curing the dual-cure composition at a temperature of from 80° C. to 130°C. for a period of time sufficient to form a cured composite.

The process for the production of a dual-cure composite may furthercomprise the additional step of: (vi) adding to said prepolymercomposition during and/or after step (i) but before step (v) component(F), which is a fibrous support material.

In another embodiment, the final density of the cured composite formedby the aforementioned process may be less than 1.20 g/ml, preferablyless than 1.15 g/ml. Further, the dual-cure composition may have a T_(g)of from −20° C. to +20° C. and the cured composite may have a T_(g) offrom 70° C. to 130° C.

The present invention also relates to a prepreg material comprising (i)at least one fibrous material support, and (ii) a dual-cure compositioncomprising components (A), (B), (C), (D), (E), optionally (G), andoptionally (H) as listed above. The fibrous material support may becarbon, aramid, glass, ceramic, quartz, boron, polyester, polyethylene,polyoxazoline or natural fibers. In another embodiment, the heat ofpolymerization of the final prepreg material may be less than 170 J/g,preferably less than 130 J/g. In further embodiments, the prepregmaterial may be converted to a composite component by exposure to atemperature of from 80° C. to 130° C. for a period of time sufficient toform a cured composite.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects, features, benefits and advantages of the embodiments hereinwill be apparent with regard to the following description, appendedclaims, and accompanying drawings.

FIG. 1 illustrates experimental viscosity profiles for various dual-curecompositions in accordance with certain aspects of the presentinvention;

FIG. 2A-2C are a series of scanning electron microscope (SEM) images at50× magnification depicting cross sections of composites formed using(a) a dual-cure composition in accordance with certain aspects of thepresent invention and (b, c) epoxy compositions of the prior art; and

FIG. 3A-3B are a series of scanning electron microscope (SEM) images at400× magnification depicting cross sections of composites formed using(a) a dual-cure composition in accordance with certain aspects of thepresent invention and (b, c) epoxy compositions of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of the following detailed description, it is to beunderstood that the present invention may assume various alternativevariations and step sequences, except where expressly specified to thecontrary. Moreover, other than in any operating examples, or whereotherwise indicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the invention are approximations, thenumerical values set forth in the specific examples are reported asprecisely as possible. Any numerical value, however, inherently containscertain errors necessarily resulting from the standard variation foundin their respective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances:

In the following description, the present invention is set forth in thecontext of various alternative embodiments and implementations involvinga dual-cure composition which may be used as the matrix in a prepregmaterial, a prepreg material comprising the dual-cure composition and afibrous support, and methods for producing the dual-cure composition,the prepreg material comprising said dual-cure composition, andcomposite components made from the prepreg material. The term “prepreg”as used herein preferably refers to a composite, whether in rod, rope,fiber, roving, strand, tow, sheet, or other form, which comprises areinforcing fiber or other such substrate (support) impregnated with aresin or polymer composition (matrix).

The dual-cure composition of the present invention cures at temperaturesbetween 80-130° C. and consist essentially of:

a multifunctional polyol,

a curing agent containing uretidione groups,

a low viscosity unsaturated reactive diluent,

at least one reactively activatable catalyst,

a thermal crosslinking initiator, optionally,

an epoxy acid scavenger; and optionally

an acrylate co-catalyst

As compared to the standard matrix materials used in prepregs of theprior art, the dual-cure composition of the present invention exhibitsseveral advantages. One major advantage is a lower cure temperature. Thedual-cure composition of the present invention may be cured attemperatures between 80 and 130° C., yet may exhibit a long roomtemperature shelf-life of several months and a cold stored shelf-life ofgreater than six months.

Another major advantage is a much lower exotherm. The dual-curecomposition of the present invention may release ≦130 J/g as compared totypical epoxy resins that release an exotherm on the order of 300 J/g.The lower exotherm may result in increased productivity for thecomposite manufacturer due to the ability to rapidly increase the curingtemperature without releasing the exotherm all at once and therebyoverheating the support, the matrix, or the molds and even scorching thefinal composite. For example, the dual-cure composition of the presentinvention may be safely cured at a temperature of 130° C. with anincreased ramp rate 5° C./minute). In addition, the lower exotherm ofthe dual-cure composition may allow for thicker/larger composite partsfabrication, as multiple layers of prepreg may be used to buildstrength.

Moreover, the dual-cure composition of the present invention hasconsiderably better fiber wet out properties than the prior art matrixmaterials. The improved fiber wet out, which may lead to improvedmechanical strength in the final composite components, can be assessedvisually by scanning electron microscopy (SEM). FIGS. 2 and 3 show aseries of SEM micrographs at 50× and 400× magnification for crosssections of composites formed using a dual-cure composition of thepresent invention and epoxy compositions of the prior art. FIG. 2A showsthat the glass fibers are uniformly dispersed in the composite sampleformed using the dual-cure composition of the present invention. FIGS.2B and 2C, on the other hand, show that composites formed using theepoxy compositions of the prior art have regions of non-glass fibercontaining material (voids which are filled with resin only).Furthermore, FIG. 2C shows regions where the glass fibers are clusteredtogether. Composites formed using a dual-cure composition of the presentinvention also show a greater fiber content (e.g. the glass fibers aremore tightly packed, see FIG. 3A) as compared with a composite formedusing the epoxy compositions of the prior art (FIG. 3B).

It is well known in the art that decreased mechanical strength in afiber reinforced composite component can often be traced to poor orincomplete impregnation of the reinforcing fiber with the resin matrixmaterial. Viscosity of the resin matrix material is the single mostimportant factor in good fiber wet-out: lower viscosity leads to betterfiber wet-out. Surprisingly, the components of the dual-cure compositionof the present invention are not lower viscosity than the prior artepoxy resins and yet show excellent fiber wet-out properties which aremeasurably better than the prior art epoxy resins (see FIGS. 2 and 3).

The dual-cure compositions of the present invention are formulated toimprove fiber wet-out and thus provide prepregs that may be used in themanufacture of composite components with exceptional mechanical strengthand dimensional stability. The enhanced fiber wet out may also lower thematrix material demand in the composite component, resulting in higherfiber volume while still maintaining acceptable levels of adhesionbetween the dual-cure composition and the fibers.

Once cured, the dual-cure composition of the present invention has amuch lower density than prior art matrix materials. For example, thedual-cure composition of the present invention may have a density ofless than 1.20 g/ml, preferably less than 1.15 g/mL once cured resultingin significant weight and cost savings as compared to the prior artepoxy resins with densities of 1.20 g/ml or greater. Furthermore, alower density may result in decreased exotherms by reducing the resinweight at a given fiber volume.

The dual-cure composition of the present invention has been found toexhibit at least two thermal transitions, as measured by dynamicmechanical analysis, corresponding to the relaxation in the uretidioneand free radically-cured resin glass transition temperatures (T_(g)). Inaddition to the two transitions, a broadened shoulder developed on theT_(g) relaxation of the resin. This is likely due to an increasedinterphase between the resin and uretidione matrix and is indicative ofa rather complex morphology. It has been proposed from studies in otherresins (cf. Gryshchuk et al., Journal of Applied Polymer Science (2002)84, pp. 672-80) that such transitions and the broadened shouldersbetween these transitions are indicative of increased toughness in theresin. Such increased toughness may convey an increased fatigueresistance for composites made using the dual-cure composition of thepresent invention.

Prior art epoxy prepregs are not stable at room temperature and willincrease molecular weight at ambient conditions resulting in a loss oftack and drape. Thus far, we have found that prepregs formulated usingthe dual-cure composition of the present invention are stable at roomtemperature resulting in reduced transportation, storage, andpreparation (rolls of the prior art epoxy prepreg must be allowed tothaw overnight) costs. Currently, epoxy gel coats are used in the moldand the composite parts are overcoated after de-molding by pigmentedcoatings (e.g. paints) to provide more uniform color. The dual-curecomposition of the present invention may allow for increasedcompatibility with gel-coats that could eliminate the 2-step coatingprocess previously described. Furthermore, the composite's outer layercould be comprised of a resin rich pigmented matrix, allowing the gelcoat to be eliminated altogether.

Thus, a first embodiment of the present invention is a dual-curecomposition consisting essentially of: (A) a multifunctional polyol, (B)a curing agent containing uretidione groups, (C) a low viscosityunsaturated reactive diluent, (D) at least one reactively activatablecatalyst, (E) a thermal crosslinking initiator, optionally (G) an epoxyacid scavenger, and optionally (H) an acrylate co-catalyst.

Suitable as component (A) in the dual-cure composition of the presentinvention are multifunctional polyols that are either free radicallyreactive monomers or non-free radically reactive oligomers. The term“polyol” is meant to include materials having an average of two or morehydroxyl groups per molecule. As used herein, (meth)acrylate may betaken to include acrylates and methacrylates.

The free radically reactive polyols may include low molecular weightmonomers of monols, diols, triols and higher alcohols and polyols suchas vinyl ether polyols, (meth)acrylate polyols, urethane (meth)acrylatepolyols, ethoxy (meth)acrylate polyols, polyester (meth)acrylate, epoxy(meth)acrylate polyols, and polyether (meth)acrylate polyols. The term“monomer” may be taken to mean the simple unpolymerized form of achemical compound having relatively low molecular weight, e.g., amolecular weight below 5000 KDa. Preferably, low molecular weight may betaken to mean a molecular weight below 1000 KDa.

Examples of suitable free radically reactive polyols of component (A)are those containing vinyl ether, urethane, urethane acrylate, epoxyacrylate, maleyl, fumaryl, maleimide, dicyclopentadienyl, acrylamide,and (meth)acrylic groups, preference being given to vinyl ethers and/or(meth)acrylates, more preferably acrylates. Examples of suitablehydroxyl-containing compounds of component (A) are 2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, hydroxybutyl vinyl ether,3-hydroxy-2,2-dimethylpropyl (meth)acrylate, the hydroxy-functionalmono-, di- or where possible higher acrylates such as, for example,glyceryl di(meth)acrylate, trimethylolpropane di(meth)acrylate,pentaerythritol tri(meth)acrylate or dipentaerythritolpenta(meth)acrylate, which are obtainable by reacting polyhydric,optionally alkoxylated alcohols such as trimethylolpropane, glycerol,pentaerythritol, dipentaerythritol.

Likewise, suitable as component (A) as well are alcohols obtained fromthe reaction of acids containing double bonds with epoxide compoundsoptionally containing double bonds, such as, for example, the reactionproducts of (meth)acrylic acid with glycidyl (meth)acrylate or bisphenolA diglycidyl ether. Additionally it is likewise possible to useunsaturated alcohols which are obtained from the reaction of optionallyunsaturated acid anhydrides with hydroxy compounds and epoxide compoundsthat optionally contain acrylate groups. By way of example these are thereaction products of maleic anhydride with 2-hydroxyethyl (meth)acrylateand glycidyl (meth)acrylate. Preferred commercially available examplesof such include the difunctional bisphenol A based epoxy acrylateSartomer CN120 offered by Sartomer Company (Exton, Pa.), the epoxyacrylates Ebecryl® offered by Cytec Industries Inc., and the unsaturatedaromatic epoxy acrylate Desmolux™ VP LS 2266 offered by BayerMaterialScience, LLC (Pittsburgh, Pa.).

Suitable polyester (meth)acrylates include polycondensation products ofdicarboxylic or oligocarboxylic acids or the anhydrides thereof (forexample, adipic acid, sebacic acid, maleic anhydride, fumaric acid andphthalic acid) and difunctional polyols and/or polyols of higherfunctionality (e.g. ethylene glycol, propylene glycol, diethyleneglycol, trimethylolpropane, pentaerythritol, alkoxylated diols orpolyols, such as the addition product of ethylene oxide ontrimethylolpropane with a hydroxyl value of 550) and (meth)acrylic acid.Alternatively, the polyester (meth)acrylates may includepolycondensation products of dicarboxylic or oligocarboxylic acids orthe anhydrides thereof and hydroxyl acrylates or epoxy acrylates (e.g.hydroxy ethyl acrylate or glycidyl methacrylate). The production ofpolyester acrylates is described in DE-A-4 040 290, DE-A-3 316 592, P.K. T. Oldring (Ed.), Chemistry & Technology of UV & EB Formulations forCoatings, Inks & Paints, Vol. 2, 1991, SITA Technology, London, pp123-135.

Alternatively, known poly-epoxy acrylates containing hydroxyl groups orpolyurethane acrylates containing hydroxyl groups may also be employed,as well as mixtures thereof with one another and with unsaturated and/orsaturated polyesters containing hydroxyl groups. One commerciallyavailable hydroxy ethyl acrylate is Tone® M-100 offered by DowChemicals.

In certain embodiments of the dual-cure composition of the presentinvention, component (A) may be a multifunctional polyol which is anon-free radically reactive oligomer with functionality greater than 2,preferable greater than 3. Examples of suitable non-free radicallyreactive oligomers of component (A) includes polyester polyols,polyether polyols, or low molecular weight polyols such as, for example,ethylene glycol, 1,2- and 1,3-propanediol, isomeric butanediols,neopentyl glycol, 1,6-hexanediol, 2-methyl-1,3-propanediol,2,2,4-trimethyl-1,3-pentanediol, 2-n-butyl-2-ethyl-1,3-propanediol,glycerol monoalkanoates (such as for example glycerol monostearates),dimer fatty alcohols, diethylene glycol, triethylene glycol,tetraethylene glycol, 1,4-dimethylolcyclohexane, dodecanediol,alkoxylated bisphenol A, hydrogenated bisphenol A, 1,3-hexanediol,1,3-octanediol, 1,3-decandiol, 3-methyl-1,5-pentanediol,3,3-dimethyl-1,2-butanediol, 2-methyl-1,3-pentanediol,2-methyl-2,4-pentanediol, 3-hydroxymethyl-4-heptanol,2-hydroxymethyl-2,3-dimethyl-1-pentanol, glycerol, trimethylolethane,trimethylolpropane, timer fatty alcohols, isomeric hexanetriols,sorbitol, pentaerythritol, ditrimethylolpropane, dipentaerythritol,diglycerol and 4,8-bis(hydroxymethyl)-tricyclo[5.2.0^(2.6)]-decane (TCDalcohol).

Suitable polyester polyols include, for example, the reaction productsof polyhydric, preferably dihydric alcohols (optionally in the presenceof trihydric alcohols), with polyvalent, preferably divalent, carboxylicacids. Instead of using the free carboxylic acids, it is also possibleto use the corresponding polycarboxylic acid anhydrides or correspondingpolycarboxylic acid esters of lower alcohols or mixtures thereof forproducing the polyesters. The polycarboxylic acids may be aliphatic,cycloaliphatic, aromatic, and/or heterocyclic and may be unsaturated orsubstituted, for example, by halogen atoms. A preferred commerciallyavailable example of one such component (A) is the polyester polyolDesmophen® 2035 offered by Bayer MaterialScience LLC (Pittsburgh, Pa.).

Suitable polyether polyols may be prepared by the reaction of suitablestarting compounds which contain reactive hydrogen atoms with alkyleneoxides such as, for example, ethylene oxide, propylene oxide, butyleneoxide, styrene oxide, tetrahydrofuran, epichlorohydrin, and mixturesthereof. Suitable starting compounds containing reactive hydrogen atomsinclude compounds such as, for example, ethylene glycol, propyleneglycol, butylene glycol, hexanediol, octanediol, neopentyl glycol,cyclohexanedimethanol, 2-methyl-1,3-propanediol,2,2,4-trimethyl-1,3-pentanediol, triethylene glycol, tetraethyleneglycol, polyethylene glycol, dipropylene glycol, polypropylene glycol,dibutylene glycol, polybutylene glycol, glycerine, trimethylolpropane,pentaerythritol, water, methanol, ethanol, 1,2,6-hexane triol,1,2,4-butane triol, trimethylolethane, mannitol, sorbitol, methylglycoside, sucrose, phenol, resorcinol, hydroquinone, 1,1,1- or1,1,2-tris-(hydroxyphenyl)-ethane, etc.

Preferable polyether polyols include, for example, polyoxyethyleneglycol, polyoxypropylene glycol, polyoxybutylene glycol,polytetramethylene glycol, block copolymers, for example, combinationsof polyoxypropylene and polyoxyethylene glycols, poly-1,2-oxybutyleneand polyoxyethylene glycols, poly-1,4-oxybutylene and polyoxyethyleneglycols, and random copolymer glycols prepared from blends of two ormore alkylene oxides or by the sequential addition of two or morealkylene oxides. Particularly preferred low viscosity multifunctionalnon-free radically reactive polyols are the propylene oxide basedpolyols with hydroxyl numbers greater than 225, preferably with hydroxylnumbers greater than 500. Preferred commercially available examples ofsuch component (A) are the polyether polyol MULTRANOL® 9170 and Arcol®LG-650 offered by Bayer MaterialScience LLC (Pittsburgh, Pa.), andPluracol® TP 340 offered by BASF Corporation (North America).

Suitable as component (B) in the dual-cure composition of the presentinvention are aromatic or (cyclo)aliphatic diisocyanates orpolyisocyanates containing uretidione groups. As used herein, aliphaticand cycloaliphatic are designated as (cyclo)aliphatic. The diisocyanatesor polyisocyanates containing uretidione rings (dimeric diisocyanates ordimeric polyisocyanates) used in the present invention are preferablysolids with melting points above 40° C. but preferably below 100° C.,more preferably below 80° C. Mixtures of such diisocyanates orpolyisocyanates may also be used.

Examples of suitable diisocyanates or polyisocyanates include butylenediisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate(IPDI), 2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate, theisomeric bis(4,4-isocyanatocyclohexyl)methanes (H₁₂MDI),isocyanatomethyl-1,8-octane diisocyanate, 1,4-cyclohexylenediisocyanate, the isomeric cyclohexanedimethylene diisocyanates,1,4-phenylene diisocyanate (PDI), 2,4- and/or 2,6-tolylene diisocyanate(TDI), m-xylene diisocyanate (XDI), 1,5-naphthylene diisocyanate, 2,4′-or 4,4′-diphenylmethane diisocyanate (MDI), triphenylmethane4,4′,4″-triisocyanate or polyisocyanate adducts prepared from thesediisocyanates and polyisocyanates and may contain additional urethane,urea, carbodiimide, acylurea, isocyanurate, allophanate, biuret,oxadiazinetrione, uretidione, iminooxadiazine dione groups, and mixturesthereof.

Preferred diisocyanates or polyisocyanates containing uretidione groupsare IPDI, HDI, MDI, TDI and H₁₂MDI. Particularly preferred diisocyanatesor polyisocyanates containing uretidione groups are IPDI and HDI.Preferred commercially available examples of such component (B) are thecycloaliphatic polyuretidione CRELAN® EF 403 offered by BayerMaterialScience LLC (Pittsburgh, Pa.), and Vestagon® 1321 and 1540offered by Evonik Degussa Corporation (Parsippany, N.J.).

The preparation of uretidione diisocyanates and polyisocyanates from thecorresponding diisocyanates and polyisocyanates is well known in theart. An overview of isocyanate oligomerization is given in J. Prakt.Chem./Chem. Ztg. 1994, 336, 185-200. For example, uretidionediisocyanates have been prepared by dimerization of the above-mentioneddiisocyanates and polyisocyanates with catalysts such astrialkylphosphites (DE-OS 2,349,726), peralkylated carbamoylphosphines(U.S. Pat. No. 3,290,288), peralkylated aminophosphines (U.S. Pat. No.3,290,288), tertiary phosphines (U.S. Pat. No. 8,058,382), pyridines(U.S. Pat. No. 8,134,014), dialkylarylphosphines andalkyldiarylphosphines (U.S. Pat. No. 2,671,082), to name a few.

Suitable as component (C) in the dual-cure composition of the presentinvention are low viscosity unsaturated reactive diluents, such as(meth)acrylates, urethanes, siloxanes, esters, carbonates, epoxies andethers containing groups which react, with polymerization, withethylenically unsaturated compounds through exposure to free radicalpolymerization. Such groups include α,β-unsaturated carboxylic acidderivatives such as (meth)acrylates, maleates, fumarates, maleimides,acrylamides, vinyl ethers, propenyl ethers, allyl ethers, and compoundscontaining dicyclopentadienyl units. Preferred are acrylates andmethacrylates. Examples include the reactive diluents known in radiationcuring technology (cf. Römpp Lexikon Chemie, p. 491, 10th ed. 1998,Georg-Thieme-Verlag, Stuttgart) or the known binders from radiationcuring technology, such as polyether acrylates, polyester acrylates,urethane acrylates, epoxy acrylates, melamine acrylates, siliconeacrylates, polycarbonate acrylates and acrylated polyacrylates.Preferred commercially available examples of component (C) are theunsaturated aliphatic allophanate urethane acrylate Desmolux® XP 2738offered by Bayer MaterialScience LLC (Pittsburgh, Pa.) or theethoxylated bisphenol A dimethacrylate Sartomer SR540 offered bySartomer Company (Exton, Pa.). Both have low viscosities (shearviscosity at 23° C. of 530,000 mPa·s).

Suitable as component (D) in the dual-cure composition of the presentinvention are catalysts that may be metallo-organic compounds of thegeneral formula:

R₂MeX₂

in which Me means a metal, R means an alkyl residue, and X means acarboxylate or alcoholate residue, as well as metallo-organic compoundsof the general formula:

ZnMe

in which Me means a metal, Z means an acteylacetonate residue, and n=2or 3. Further, any unspecified mixtures of such metallo-organiccatalysts may be suitable as component (D).

Metal containing catalysts suitable as component (D) further include anyorganic or inorganic metal salt such as, for example, salts of zinc(II),calcium, magnesium, aluminum(III), zirconium(IV), iron(III), tin(II),organitin(IV) such as dibutyltin(IV), and molybdenum. Examples of suchmetal salts include, at least, iron(III) chloride, tin(II) octoate,tin(II) ethylcaproate, tin(II) palmitate, dibutyltin(IV) dilaurate,dibutyltin(IV) diacetate and molybdenum glycolate, zinc(II)acetylacetonate, calcium acetylacetonate, magnesium acetylacetonate,aluminum(III) acetylacetonate, zirconium(IV) acetylacetonate, and ormixtures thereof.

Preferable catalysts useful as component (D) are zinc compounds, such aszinc oxide, zinc sulphide, zinc carbonate, zinc fluoride, zinc chloride,zinc bromide, zinc iodide, zinc phosphate, zinc borate, zinc titanate,zinc hexafluorosilicate, zinc sulphite, zinc sulphate, zinc nitrate,zinc tetrafluoroborate, zinc acetate, zinc octoate, zinccyclohexanebutyrate, zinc laurate, zinc palmitate, zinc stearate, zincbeherate, zinc citrate, zinc gluconate, zinc acetylacetonate, zinc2,2,6,6-tetramethyl-3,5-heptanedionate, zinc trifluoracetate, zinctrifluoromethane-sulphonate, zinc dimethyldithiocarbamate and mixturesof these compounds. More preferred as component (D) is zincacetylacetonate.

Additional catalysts useful as component (D) may further includetetralkylammonium salts and/or phosphonium salts with halogens, withhydroxides, with alcoholates or with organic or inorganic acid anions ascounter-ion. Such catalysts can be added alone or in a mixture.Preferred examples of component (D) are tetrabutylammonium acetate andbenzyltrimethylammonium chloride (BMAC).

Additional catalysts useful as component (D) may further includecatalysts with an amidine structure such as, for example,1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU).

The compounds of catalyst component (D) can be dissolved advantageouslyin one of the components used in the process, or in a portion thereof.In particular, the zinc compounds for use in accordance with the presentinvention dissolve very well in the polyols of component (A), so thatcomponent (D) in solution in small amounts of component (A) can bemetered in as a concentrated solution in liquid form.

In the process of the present invention, catalyst component (D) ispreferably used in amounts of 0.001 to 10.0% by weight, more preferably0.01 to 5.0% by weight and most preferably 0.05 to 2.0% by weight, basedon the solids content of the product.

Suitable as component (E) in the dual-cure composition of the presentinvention are thermal crosslinking initiators, such as those capable ofthermal curing of activated double bonds using thermally decomposingfree-radicals initiators. The free radical polymerization reaction maybe initiated by peroxides or hydroperoxides by the addition of heat.Peroxides which can be used for the purposes of the present inventionare preferably organic peroxides with the general formula R—O—O—R whichdecompose into radicals at from 0° to 250° C., preferably from 40° to180° C., and which can be used for initiating radical polymerizationreactions. Examples include: sulphonyl peroxides, such as acetylcyclohexane sulphonyl peroxide; percarbonates, such as dicyclohexylperoxy dicarbonate; di-n-butyl peroxy dicarbonate and diisopropyl peroxydicarbonate; peresters, such as tert.-butyl peroxy pivalate, tert.-butylperneodecanoate and tert.-butyl perbenzoate; diacyl peroxides, such asbis-(3,3,5-trimethyl-hexanoyl)-peroxide; dilauroyl peroxide; didecanoylperoxide, dipropionyl peroxide; bis-(2,4-dichlorobenzoyl)-peroxide anddibenzoyl peroxide; dialkyl peroxides, such as dicumyl peroxide anddi-tert.-butyl peroxide; ketal peroxides, such as 1,1-di-tert.-butylperoxy-3,3,5-trimethyl cyclohexane; alkyl hydroperoxides, such as cumenehydroperoxide and tert.-butyl hydroperoxide, and ketone peroxides, suchas cyclohexanone peroxide and ethyl methyl ketone peroxide.

Further, the free radical polymerization reaction may be initiated bypercarboxylic acid esters and azo compounds by the addition of heat. Thepercarboxylic acid esters include compounds such as tertiary butylperoctoate and tertiary butyl perpivalate. The azo compounds includecompounds such as 2,2′-azo-bis-isobutyronitrile (AIBN),2,2′-azo-bis-2-methyl-butyronitrile,1,1′-azo-dicyclopentane-carbonitrile,1,1′-azo-dicyclohexane-carbonitrile,2,2′-azo-bis-cyclopentylpropionitrile, 1,1′-azo-dicampher-carbonitrile,2,2′-azo-bis(α,γ-dimethyl-valeronitrile),2,2′-azo-bis-2-phenylpropionitrile, 2,2′-azo-bis-2-benzyl-propionitrileand 2,2′-azo-bis-2-(4-methoxyphenyl)-propionitrile.

It is desirable that the thermal crosslinking initiators decompositionrate may be fairly high, i.e., that the half-life period of thermaldecomposition be short enough under the polymerization conditions toensure that an adequate supply of radicals is available in the reactionmixture. Preferred initiators thus include, for example, organicperoxides, such as benzoyl peroxide or lauroyl peroxide, and diacylperoxides such as ducumyl peroxide.

Also suitable as component (E) in the dual-cure composition of thepresent invention are initiators which can be activated by actinicradiation and which trigger free-radical polymerization of thecorresponding polymerizable groups. Photoinitiators activated by UV orvisible light are preferred. Photoinitiators are known and include bothunimolecular (type I) and bimolecular (type II) initiators. Suitable(type I) systems include aromatic ketone compounds, e.g. benzophenonesin combination with tertiary amines, alkylbenzophenones,4,4′-bis(dimethylamino)benzophenone (Michler's ketone), anthrone,halogenated benzophenones or mixtures thereof. Also suitable are (typeII) initiators such as benzoin and its derivatives, benzil ketals,acylphosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphineoxide, bisacylphosphine oxides, phenylglyoxylic esters, camphorquinone,α-aminoalkylphenones, α,α-dialkoxyacetophenones andα-hydroxyalkylphenones. Where the coating composition of the inventionis to be processed on an aqueous basis, it is preferred to usephotoinitiators which can be readily incorporated into aqueous coatingcompositions. Examples of such products include Irgacure® 500, Irgacure®819 DW (Ciba, Lampertheim, DE) and Esacure® KIP (Lamberti, Aldizzate,Italy). Mixtures of these compounds can also be used.

In the process of the present invention, thermal crosslinking initiatorcomponent (E) is preferably used in amounts of 0.001 to 10.0% by weight,more preferably 0.01 to 5.0% by weight and most preferably 0.05 to 2.0%by weight, based on the solids content of the product.

In certain embodiments of the dual-cure composition of the presentinvention, the components may be mixed in ratios that provide from 15 to45% by weight of component (A), from 25 to 75% by weight of component(B), and from 15 to 55% by weight of component (C), based on the solidscontent of the product.

The relative amounts of component (A) and component (B) can varysomewhat depending on their respective molecular weights. Typically,they can each be present in amounts within the range of 10 to 90% byweight based on resin solids weight of the components. The equivalentratio of hydroxyl to uretidione is typically from 0.5:1.0 to 2.0:1,preferably from 0.8:1 to 1.1:1 and most preferable from 0.8:1 to 0.9:1.

Furthermore, the dual-cure composition of the present invention mayoptionally comprise additional epoxy functional molecules and acrylateco-catalysts. As such, embodiments of the dual-cure composition mayfurther comprise component (G) which is an epoxy functional molecule andcomponent (H) which is an acrylate co-catalyst.

Suitable as component (G) in the dual-cure composition of the presentinvention are epoxy functional molecules which may act as acidscavengers. Any chemical compound which contains the epoxide (oxirane)functionality is most suitable as the acid scavenger in the presentinvention. The term “epoxide” or “epoxy”, as used herein, refers to anyorganic compound or resin containing at least one group comprising athree membered oxirane ring. Preferably two or more oxirane groups arepresent in the epoxide compound or resin in order to obtain thepolyisocyanate compositions with consistent reactivity profiles of thepresent invention. The epoxide equivalent weight (EEW) range of suitableepoxides is from about 44 to 400, preferably 100 to 350 and mostpreferably 150 to 300. Both aromatic and aliphatic polyepoxides may beused, and are well known. Suitable epoxides are described in U.S. Pat.No. 5,726,240.

Thus, suitable as component (G) are glycidyl ethers, glycidyl esters,aliphatic epoxides, diglycidyl ethers based on bisphenol A, glycidyl(meth)acrylates, alone or in a mixture. Further examples are monoepoxidecompounds or polyfunctional epoxides, in particular di- or trifunctionalepoxides. Examples include epoxidized olefins, glycidyl ethers of(cyclo)aliphatic or aromatic polyols and/or glycidyl esters of saturatedor unsaturated carboxylic acids. Preferred monoepoxide compounds includeglycidyl (meth)acrylate, the glycidyl ester of versatic acid,butyl-glycidyl ether, 2-ethylhexyl-glycidyl ether, phenyl-glycidylether, o-cresyl-glycidyl ether or 1,2-epoxybutane. Glycidyl methacrylateis preferred. Preferred polyepoxide compounds include polyglycidylcompounds of the bisphenol A or bisphenol F type as well as theperhydrogenated derivatives thereof or glycidyl ethers of polyfunctionalalcohols such as butanediol, hexanediol, cyclohexanedimethanol,glycerol, trimethylolpropane or pentaerythritol. It is also possible touse epoxy-functional polymers of vinyl monomers such as monofunctional(meth)acrylates or styrene along with the use of a proportion of e.g.glycidyl methacrylate.

Suitable as component (H) in the dual-cure composition of the presentinvention are acrylate co-catalysts such as free radical reactivitycontrollers or radical scavengers which may allow for improved stabilityof the matrix materials prior to curing. Such compounds may inhibit freeradical reactivity below a specific temperature, and thus may stabilizethe matrix materials and prepreg when at room temperature. The radicalscavenger may comprise a nitroxide radical. Suitable nitroxide radicalsinclude, but are not limited to, SG-1 (nitroxide,1-(diethoxyphosphinyl)-2,2-dimethylpropyl 1,1-dimethylethyl freeradical); TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy free radical);PROXYL (2,2,5,5-tetramethyl-1-pyrrolidinyloxy free radical); andmixtures thereof.

TEMPO free radicals and their deriviatives may include, for example,4-hydroxy TEMPO free radical(4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy free radical);TEMPO-Polymer Bound or PS-TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyfree radical)-polymer bound; 4-(2-bromoacetamido)-TEMPO free radical(4-(2-bromoacetamido)-2,2,6,6-tetramethyl-1-piperidinyloxy freeradical); 4-(2-iodoacetamido)-TEMPO free radical(4-(2-iodoacetamido)-2,2,6,6-tetramethyl-1-piperidinyloxy free radical);4-acetamido-TEMPO free radical(4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl free radical);4-amino-TEMPO free radical (4-amino-2,2,6,6-tetramethylpiperidine-1-oxylfree radical); 4-carboxy-TEMPO free radical(4-carboxy-2,2,6,6-tetramethylpiperidinyloxy, free radical);4-hydroxy-TEMPO benzoate free radical(4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl benzoate free radical);4-maleimido-TEMPO free radical(4-maleimido-2,2,6,6-tetramethyl-1-piperidinyloxy free radical);4-methoxy-TEMPO free radical(4-methoxy-2,2,6,6-tetramethyl-1-piperidinyloxy free radical);4-oxo-TEMPO free radical (4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyfree radical); 4-phosphonooxy-TEMPO hydrate free radical(4-phosphonooxy-2,2,6,6-tetramethyl-1-piperidinyloxy, free radicalhydrate); and mixtures thereof.

PROXYL free radicals and their derivatives may include, for example,3-(2-iodoacetamido)-PROXYL free radical(3-(2-iodoacetamido)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy freeradical); 3-[2-(2-maleimidoethoxy)ethylcarbamoyl]-PROXYL free radical(3-[2-(2-maleimidoethoxy)ethylcarbamoyl]-2,2,5,5-tetramethyl-1-pyrrolidinyloxyfree radical); 3-carbamoyl-PROXYL free radical(3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy free radical);3-cyano-PROXYL free radical(3-cyano-2,2,5,5-tetramethyl-1-pyrrolidinyloxy free radical);3-maleimido-PROXYL free radical(3-maleimido-2,2,5,5-tetramethyl-1-pyrrolidinyloxy free radical);3-(2-bromo-acetoamido-methyl)-PROXYL free radical(3-(2-bromo-p-acetoamido-methyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxyfree radical); 34242-iodoacetamido)acetamido)-PROXYL free radical(3-(2-(2-iodoacetamido)acetamido)-2,2,5,5-tetramethylpyrrolidin-1-yloxyfree radical); 3-(2-isothiocyanato-ethyl-carbamoyl)-PROXYL free radical(3-(2-isothiocyanato-ethyl-carbamoyl)-2,2,5,5-tetramethylpyrrolidin-1-yloxyfree radical); 3-(3-(2-iodo-acetamido)-propyl-carbamoyl)-PROXYL freeradical(3-(3-(2-iodo-acetamido)-propyl-carbamoyl)-2,2,5,5-tetramethylpyrrolidin-1-yloxyfree radical); and mixtures thereof.

Other suitable nitroxide free radicals include, for example,16-doxyl-stearic acid methyl ester free radical;2,2,3,4,5,5-hexamethyl-3-imidazolinium-1-yloxy methyl sulfate freeradical; 2,2,6,6-tetramethyl-4-(methylsulfonyloxy)-1-piperidinooxy freeradical;4-(1-hydroxy-1-methylethyl)2,2,5,5-tetramethyl-3-imidazolinium-1-yloxyfree radical;4-phenacylidene-2,2,5,5-tetramethylimidazolidazolidin-1-yloxy freeradical; 4-phenyl-2,2,5,5-tetramethyl-3-imidazolin-1-yloxy free radical;5-DOXYL-stearic acid free radical(2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxy freeradical); methyl 5-DOXYL stearate free radical(2-(4-methoxy-4-oxobutyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxy freeradical); 1-hydroxy-2,2,4,6,6-pentamethyl-4-piperidinyl3,5-di-tert-butyl-4-hydroxybenzoate free radical;1-hydroxy-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrole-3-carboxylic acidfree radical;4-[(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)amino]-4-oxo-2-butenoicacid free radical;bis(1-hydroxy-2,2,4,6,6-pentamethyl-4-piperidinyl)oxalate free radical;tris(1-hydroxy-2,2,4,6,6-pentamethyl-4-piperidinyl)phosphinetricarboxylatefree radical; CYPMPO(2-(5,5-dimethyl-2-oxo-2-lambda-5-[1,3,2]dioxaphosphinan-2-yl)-2-methyl-3,4-dihydro-2H-pyrrole-1-oxidefree radical); 5-(2,2-dimethyl-1,3-propoxycyclophosphoryl)-5-methyl-1-pyrroline N-oxide free radical; and mixturesthereof.

Embodiments of the dual-cure composition of the present invention mayfurther comprise additional unsaturated materials that may be used toadjust the final viscosity.

Embodiments of the dual-cure composition of the present invention mayalso comprise one or more additives, such as fillers, impact modifiers,antifoaming agents, mold release agents, lubricants, thixotropes,antioxidants, UV absorbers, heat stabilizers, flame retardants,pigments, colorants, nonfibrous reinforcements and fillers,plasticizers, impact modifiers such as ionomers or maleated elastomers,and other such customary ingredients and additives. One preferredadditive is an antifoaming agent such as, for example, the silicondefoamer TEGO® AIREX 980 or 944 by Evonik Industries AG.

Another embodiment of the present invention is a process for theproduction of a dual-cure composition comprising:

homogenizing a pre-polymer composition comprising components (A), (B),(C), optionally (G), and optionally (H);

heating the pre-polymer composition to a temperature above the Tg ofcomponent (B);

cooling the heated pre-polymer composition to a temperature of less than110° C.; and

mixing components (D) and (E) into the cooled pre-polymer composition toform a dual-cure composition.

Another embodiment of the present invention is a process for theproduction of a dual-cure composite comprising the additional step of:

(v) curing the dual-cure composition as listed above at a temperature offrom 80° C. to 130° C. for a period of time sufficient to form a curedcomposite.

In additional embodiments of the process for production of a dual-curecomposition and production of a dual-cure composite, the cooling at step(iii) may be reduced to a temperature below 110° C. For example, thecomposition may be cooled to a temperature comparable to the T_(g) ofcomponent (B) or to a temperature below the T_(g) of component (B).Preferably, the composition may be cooled to a temperature of less than100° C., and more preferably to a temperature of less than 85° C.

A further embodiment of the present invention is a prepreg materialcomprising (i) at least one fibrous material support, and (ii) theaforementioned dual-cure composition. Embodiments of the prepregmaterial may use all types of fibrous material support or otherreinforcing materials commonly used in the art for these applications.It is also possible for a roving bundle or tow to be shaped before beingimpregnated, for example to be flattened to a tape, or for thereinforcing fiber to be used as a cloth. Useful fibrous materialsupports include, without limitation, glass fibers, carbon fibers,graphite fibers, polymeric fibers including aramid fibers, boronfilaments, ceramic fibers, polyester fibers, polyethylene fibers,polyoxazoline fibers, metal fibers, asbestos fibers, beryllium fibers,silica fibers, silicon carbide fibers, natural fibers, and so on. Hybridcompositions of the aforementioned fibers may be used in the prepregsand composites of the present invention. Furthermore, the fibers may beselected for specific unique characteristics beyond strength such as,for example, the fibers may be conductive. Conductive fibers, forexample conductive carbon fibers or metal fibers, may be used to producearticles for conductive or static charge dissipative applications or EMIshielding.

Glass fibers, which are very common in the art, are available in anumber of different kinds, including E-glass, ECR-glass (a modifiedE-glass that is chemically resistant), R-glass, S-glass and S-2 glass,C-glass, M-glass, AP-glass and hollow glass fibers.

The fiber filaments are usually formed into a bundle, called a roving ortow, of a given uniform cross-sectional dimension. The fibers of thebundle are usually all of the same type, although this is not essentialto the present invention. For a particular matrix composition, a fibrousmaterial support should be chosen that can withstand the temperaturesand shear suitable for producing the desired prepreg. In particular, ifa fiber is coated with a sizing or finishing material, the materialshould be one that is stable and remains on the fiber at the selectedprocessing temperature. A sizing or finishing material, if employed, maybe selected and applied according to customary means. Unsized fiberssuch as carbon are advantageously employed in some applications in orderto optimize mechanical properties.

Another embodiment of the present invention is a process for producing aprepreg material comprising:

homogenizing a pre-polymer composition comprising components (A), (B),(C), optionally (G), and optionally (H);

heating the pre-polymer composition to a temperature above the Tg ofcomponent (B);

cooling the heated pre-polymer composition to a temperature of less than110° C.;

mixing components (D) and (E) into the cooled pre-polymer composition toform a dual-cure composition; and

adding to said prepolymer composition during and/or after step (i)component (F), which is a fibrous support material.

In additional embodiments of the process for production of a prepregmaterial, the cooling at step (iii) may be reduced to a temperaturebelow 110° C. For example, the composition may be cooled to atemperature comparable to the T_(g) of component (B) or to a temperaturebelow the T_(g) of component (B). Preferably, the composition may becooled to a temperature of less than 100° C., and more preferably to atemperature of less than 85° C.

Another embodiment of the present invention is a process for producing acomposite from a prepreg material, the process comprising the additionalstep of:

(vi) curing the prepreg material at a temperature of from 80° C. to 130°C. for a period of time sufficient to form a cured composite.

In the production of the prepreg, the fiber bundle, mat, cloth, or otherfibrous support material is heated to a selected temperature above themelting point, softening point, or glass transition temperature (Tg) ofthe impregnating resin matrix composition. In many cases, this heatingis achieved by heating the rollers or other equipment used to convey thefibrous support material. The temperature to which the fibrousreinforcing material is heated may be sufficient to produce a prepreghaving no voids or substantially no voids. The temperature to which thefibrous reinforcing material is heated thus may be sufficient to causethe impregnating resin to fully or substantially fully wet out thefibrous reinforcing material.

The means for heating the fiber is not generally critical, and may bechosen from any number of means generally available for heatingmaterials. Particular examples of such means include, withoutlimitation, radiant heat, inductive heating, infrared tunnels, orheating in an oven or furnace, e.g. an electric or gas forced air oven.Insufficient heating may result in undesirable resin conglomeration atthe surface of the roving bundle, tow, or other reinforcement. Thus, thetemperature to which the roving bundle is heated should be sufficient toallow the resin to flow between the filaments or fibers to impregnatethe roving or tow in a substantially uniform way.

The methods for producing a prepreg material of the present inventionallow the pre-polymer composition or matrix to impregnate the fiberbundle instead of agglomerating at the surface of the fiber bundle. Theparticular temperature chosen will depend upon factors that would beobvious to the person of skill in the art, such as the particular typeof resin used, the denier of the fiber, and the profile or size of thebundle and can be optimized by straightforward testing according to theultimate application method. Preferably, the reinforcing material isheated above the temperature of the impregnating matrix composition.

In the formation of a prepreg material, the dual-cure composition(matrix) may be suitable for both hot melt fiber impregnation to formeither a fully or partially impregnated prepreg with appropriate tackand handling properties and or casting as a separate resin film whichcan be combined with one or more dry fabrics to form a prepreg where theresin will flow during subsequent processing to form a fully impregnatedlaminate.

EXAMPLES

The instant process is illustrated, but in no way restricted, by thefollowing examples in which the quantities quoted represent parts byweight or percentages by weight, unless otherwise stated.

Example 1 Testing of the Mix Ratios for Components (A), (B) and (C)

TABLE 1 Material Component Description Supplier Sartomer A methacrylatedSartomer CN151 diglycidyl ether Company of Bisphenol A (Exton, PA)CRELAN ® B cycloaliphatic Bayer EF 403 polyuretdione MaterialScience LLC(Pittsburgh, PA) Sartomer C ethoxylated Sartomer SR540 bisphenol ACompany dimethacrylate (Exton, PA) D Zinc acetoacetonate E dicumylperoxide

Preparation of the Dual-Cure Composition

This example illustrates the preparation of an exemplary dual-curecomposition comprising various mix ratios of component (A)+(B) withcomponent (C). Identities of such components according to embodiments ofthe present invention are listed in Table 1.350 g of a mixturecontaining 35%, 47.5%, 60%, 72.5%, 74.5%, and 85% of component (A)+(B)relative to component (C) was put into a cup and mixed in a Flacktekspin mixer, first at 2700 rpm for ten minutes and then at 3300 rpm forfive minutes. Free catalyst [component (D)+component (E)] was added to afinal of 1% each by weight and the mixture was spun at 3300 rpm for anadditional five minutes.

Testing

Samples were taken for analysis following (1) ASTM D3418-08: StandardTest Method for Transition Temperatures and Enthalpies of Fusion andCrystallization of Polymers by Differential Scanning calorimetry (DSC);(2) ASTM D638-10: Standard Test Method for Tensile Properties ofPlastics; and (3) ASTM D4473-08: ASTM D4473-08 Standard Test Method forPlastics: Dynamic Mechanical Properties: Cure Behavior.

TABLE 2 Results of DSC analysis Initial Enthalpy Final T_(g) % A + BT_(g) (° C.) (J/g) (° C.) 35 −35.33 ± 0.67 99.88 ± 24.82 56.24 ± 0.3247.5 −28.47 ± 0.93 92.01 ± 3.05 57.83 ± 2.07 60 −18.84 ± 0.96 76.61 ±24.23 55.43 ± 2.28 72.5  −8.72 ± 2.30 78.22 ± 16.19 56.47 ± 1.34 85 3.82 ± 5.01 49.54 ± 6.18 55.41 ± 5.90

The DSC measurements were taken using a heat profile that included 50°C./minute temperature ramps from a starting temperature of 20° C., downto −50° C., and up to 120° C. where the temperature was maintained for45 minutes. Table 2 lists values for initial glass transitiontemperature (initial T_(g)), enthalpy and final glass transitiontemperature (final T_(g)) which are averages of single measurements from3 to 4 individual samples. The initial glass transition temperatures(initial T_(g)) of the uncured resin blends at varying compositionsdemonstrates a linear relationship (r²=0.968): Increased percentcomponent (A)+(B) increases the initial T_(g).

Beyond demonstrating strength characteristics, the initial T_(g) mayalso be helpful in tracking the degradation and long term stability of aresin matrix by retesting a sample at different time periods. A singlesample of the 72.5% composition was retested at two-weeks: The initialT_(g) of the sample was found to be −6.17° C., while the retest twoweeks later found an initial T_(g) of −6.29° C.

As shown in Table 2, the DSC measurements for the dual-cure compositionsyielded T_(g) values that range from about −35 to 4° C. An optimalinitial Tg (prior to final cure to form the composite article) of about0° C. was selected to provide some tackiness to the prepreg materialwhich may aid in formation of the final composite article. For example,some tackiness in the prepreg sheets may help when several sheets arebeing aligned in or on a mold.

Enthalpy values determined from the DSC analysis show a linearrelationship with varied amounts of component (A)+(B) (r²=0.804):Increased percent component (A)+(B) decreases the enthalpy. One mightthink that this trend is backwards: more crosslinking component (B)should mean that more bonds are formed and thus the enthalpy wouldincrease. However, at a certain point, the amount of crosslinker will bein excess over component (C). Only a certain number of reactions willoccur before the only unmatched component left in the dual-curecomposition is the crosslinker component (B). The initial rapid increasein enthalpy with increasing proportions of component (A)+(B) has likelyalready occurred prior to the 35% sample. Furthermore, the dual-curecompositions of the present invention demonstrate much lower enthalpies(50 J/g to 100 J/g) than the prior art resins which typically haveenthalpies of 270 J/g or greater.

The final T_(g) for all of the tested compositions is found to beessentially independent of the proportion of component (A)+(B) in thefinal dual-cure composition (r²=0.021). Furthermore, the absolute valuesof the final T_(g) (50° C. and 60° C.) appear to be rather low andlikely represent the T_(g) of the crosslinking component (B).

Dynamic mechanical analysis (DMA) was used to more accurately determinethe final T_(g). The uncured dual-cure composition prepared above waspoured evenly into a preheated mold at 80° C. and placed into a vacuumoven at 80° C. at 30 inches of mercury (in. Hg) for 30 minutes. Thesample was then cured at 130° C. for 120 minutes under vacuum, followedby a cool cycle prior to DMA and tensile properties testing. Table 3lists values for the storage modulus onset temperature, final T_(g) andTan Delta Peak temperatures.

TABLE 3 Results of DMA testing Storage Modulus T_(g) Tan Delta Peak %A + B (° C.) (° C.) (° C.) 35 71.3 74.2 115.7 35 67 78.2 116.1 47.5 4359.4 115.2 47.5 44.3 40.1 115.2 60 52.6 66.8 119.9 72.5 57.6 53.8 113.974.5 60 61.4 108.3 85 63.8 64.8 109.6

There is no overall trend observed in the data collected for the variedpercent component (A)+(B) composition. The storage onset modulustemperature is highest for the 35% component (A)+(B) composition, butthen drops significantly before starting a steady increase in value forincreasing percent component (A)+(B) compositions. The T_(g) asdetermined by the loss modulus also seem to be quite random, with nodiscernible trend apparent. However, the overall average values of thesedata may be relied upon for comparison purposes. The average storagemodulus onset temperature for all the samples is 57.45° C., and theaverage T_(g) from loss modulus is 62.34° C. These values are similar tothe final T_(g) obtained by DSC testing, indicating that the data isconsistent across different methods of thermal testing. Thus, theaverage storage modulus onset temperature and the average T_(g) asdetermined by DMA are likely representative of the T_(g) for thecrosslinking component (B).

The data in Tables 2 and 3, taken together, indicate that the twotransitions observed in the DMA analysis are those of the acryliccomponent (A) and the uretidione component (B) of the dual-curecomposition. While the DSC is only capable of detecting the firsttransition, corresponding to the uretidione transition at 60° C., themore sensitive DMA analysis detects both the uretidione transition at60° C. and the acrylic transition at 110° C. It is likely that the twoseparate transitions observed provide improved impact strength for thefinal composite component as the cured polymer may have two differentrelaxation mechanisms. In fact, the lower temperature transition mayresult in an increased fracture toughness that may convey an increasedfatigue resistance. This may be likened to the method by which impactmodifiers or tougheners function. A discussion of such is provided inthe literature (cf. Gryshchuk et al., Journal of Applied Polymer Science(2002) 84, pp. 672-80) and discussed above.

The tan delta peak temperature data on the other hand is probably themost helpful: The reported final T_(g) values as measured by the tandelta peak using DMA are likely representative of the final curedmaterial. All values appear to be 110° C. or higher.

FIG. 1 shows viscosity profiles for the varied percent component (A)+(B)compositions. At the pre-cure temperature (above T_(g) of component(B)), the viscosities of all of the compositions are relatively low,thus providing a matrix material that may demonstrate excellent fiberwet-out properties in a prepreg material.

Table 4 lists values for tensile strength testing. Modulus values andtensile strengths for samples of varied percentage component (A)+(B)compositions appear to decrease with increasing percentage of component(A)+(B).

TABLE 4 Results of tensile strength testing Ultimate Tensile TensileTensile Elongation Elongation Modulus Strength at Strength at Strength %A + B Trial # at break (%) at Yield (%) (MPa) Break (MPa) Yield (MPa)

60 1 2.1 2.1 3070 60.5 60.5 60.5 2 1.7 1.7 3140 49.6 49.6 49.6 3 2.63060 70.3 70.3 4 3.2 3.2 3220 80.2 80.2 80.2 5 3 3190 80.5 80.5 Average2.5 2.3 3136 68.2 63.4 68.2 Std. Dev. 0.6 0.8 70.9 13.3 15.5 13.3 72.5 13.5 3.5 2910 82.9 82.9 82.9 2 1.2 1.2 3160 34.5 34.5 34.5 3 2.6 305070.1 70.1 4 2.4 3070 66.3 66.3 5 2.5 2.5 2700 63.0 63 63 Average 2.4 2.42978 63.4 60.1 63.4 Std. Dev. 0.8 1.2 179.4 17.8 24.3 17.8 74.5 1 1.51.5 2640 38.1 38.1 38.1 2 1.3 2670 32.7 32.7 3 1.8 1.8 2690 44.6 44.644.6 4 1.5 1.5 2890 41.1 41.1 41.1 5 1.9 1.9 2710 48.1 48.1 48.1 Average1.6 1.7 2720 40.9 43.0 40.9 Std. Dev. 0.3 0.2 98.5 5.9 4.3 5.9

indicates data missing or illegible when filed

Example 2 Testing of Resin Stability

A sample of the dual-cure composition formulated as a prepreg materialwas stored in the freezer or at room temperature. Viscosity profiles forthe two samples were tested after 44 days of storage and the viscosityminimum occurred for both at similar temperatures and viscosities(frozen sample: η=15.873 Pa·s, T=95.7° C.; room temperature sample:η=12.044 Pa·s, T=99.4° C.). Thus, the room temperature storage stabilityof the dual-cure composition of the present invention is greater than 44days.

Further DSC testing was performed to determine initial T_(g) values andreactivity for samples of the dual-cure composition formulated as aprepreg material which were stored in the freezer (with or withoutdesiccant) or at room temperature. DSC heating curves were generated foreach storage condition over a month long time course. The DSC methodemployed for all data presented in Table 5 used approximately 4 mgsamples which were encapsulated in vented AI DSC pans with a heatingprofile as follows: (1) cool to −40° C./hold 10 min to equilibrate; (2)heat to 50° C. @ 5° C./min and hold 5 min; (3) cool to −40° C. @ 10°/minand hold 5 min; (4) heat to 200° C. @ 5° C./min and hold 1 min; (5) coolto −40° C. @ 10° C./min and hold 5 min; and (6) heat to 200° C. @ 10°C./min. The T_(g) and reactivity data (Table 5) were taken from step 4,which is the first full heating curve to 200° C. The first peak in thebimodal reaction was integrated over the range of 100° C. to 150° C.

There does not appear to be significant variation in the roomtemperature aged sample as a function of time. Furthermore, the samplesaged at room temperature show similar T_(g) and reactivity profiles asthe samples stored frozen with or without desiccant. The roomtemperature aged sample was analyzed on day 1, 6, 20, and 34, while thesamples stored in the freezer were analyzed on day 6 (without desiccant)and on day 33 (with desiccant).

TABLE 5 Results of storage stability testing Tg ΔCp T_(rxn) ΔH_(rxn)Sample (° C.) (J/g° C.) (° C.) (J/g) Room Temperature Storage Day 1 −50.43 119 138 Day 20 −6 0.42 119 136 Day 20 −5 0.44 119 136 Day 20 −40.42 119 133 Day 34 −5 0.46 120 136 Day 34 −4 0.42 118 136 Day 34 −40.41 119 133 Frozen Storage (without desiccant) Day 6 −4 0.42 119 132Day 6 −5 0.40 122 135 Day 6 −5 0.46 123 134 Frozen Storage (withdesiccant) Day 33 −5 0.46 121 135 Day 33 −5 0.46 123 135

Example 3 Testing of Various Components (A)+(B) and Mix Ratios

Table 6 lists values for tensile strength testing on samples of variedpercentage component (A)+(B) compositions.

TABLE 6 Results of tensile strength testing Flex Flex Tensile TensileElongation- Shore D Modulus Strength Modulus Strength to- DescriptionHardness (MPa) (MPa) (MPa) (MPa) break (%) Bisphenol A Ethoxylate Diol85 — — 2596 65.9 3.2 Vestagon® 1321* Ratio OH:uretdione - 1.41:1Bisphenol A Ethoxylate Diol 85 2156 78.2 2336 28.8 1.4 (B) Crelan® 403**Ratio OH:uretdione - 1.5:1 IBOMA/Desmolux® 86 2423 109 2356 66.8 4.12738/HEMA*** + Polyol 4290^(†) Crelan® 403 Ratio OH:uretdione - 1.5:1IBOMA^(§)/Desmolux® 85 2578 110 2784 21.4 0.9 2738****/HEMA*** + Polyol4290^(†) Crelan® 403 Ratio OH:uretdione - 2:1 Desmophen® 2035^(‡) 782185 76.4 2182 37.4 1.8 Crelan® 403 Ratio OH:uretdione - 1.5:1*Vestagon® 1321 supplied by Evonik DeGussa, GmbH; **see Table 1;^(†)Polyol 4290 supplied by Perstop; ^(§)IBOMA is isobornylmethacrylate; ***Hema is Hydroxyethyl methacrylate; **** Desmolux® XP2738 supplied by Bayer Material Science LLC; ^(‡)Desmophen® 2035supplied by Bayer Material Science LLC.

Example 4 Preparation of an Alternative Dual-Cure Composition

This example illustrates the preparation of an exemplary dual-curecomposition comprising an alternate component (A), a multifunctionalpolyol which is a non-free radically reactive oligomer. Identities ofeach component according to an embodiment of the present invention arelisted in Table 7. The mix ratios are illustrated in Table 8.

TABLE 7 Material Component Description Supplier Mutranol ® A Lowmolecular- Bayer MaterialScience 9133 weight LLC (Pittsburgh, PA)polypropylene oxide-based triol CRELAN ® B cycloaliphatic BayerMaterialScience EF 403 polyuretdione LLC (Pittsburgh, PA) Desmolux ® Cunsaturated aliphatic Bayer MaterialScience XP 2738 allophanate LLC(Pittsburgh, PA) urethane acrylate D Zinc acetoacetonate E dicumylperoxide

TABLE 8 Dual-Cure Composition Weight Volume Raw material Weight Volumesolids solids Multranol 9133 11.47 1.20 11.47 1.2 Crelan ® 403 123.7613.48 123.76 13.48 Desmolux ® XP 2738 155.59 16.21 155.59 16.21 Zincaceylacetonate 6.06 0.45 6.06 0.45 Dicumyl peroxide 2.29 0.18 2.29 0.18Tego ® Airex 980 0.08 0.01 0.08 0.08 tert-Butyl peroxybenzoate 0.76 0.090.76 0.09 Total 300 31.61 300 31.61 Theoretical Results Weight 100Wt/gal 9.49 Solids Mix ratio — Volume 100 (volume) Solids NCO:OH 1.86P/B 0 Theoretical 0 PVC 0 VOC

Example 5 Testing of Various Mix Ratios of Components (A)+(B)

Table 9 lists values for tensile strength testing on samples of variedpercentage component (A)+(B) compositions, where (A) is a Bisphenol Aacrylate and (B) is Crelan® 403 (see Table 1).

TABLE 9 Results of tensile strength testing Flex Flex Tensile TensileElongation- Modulus Strength Modulus Strength to-break Description (MPa)(MPa) (MPa) (MPa) (%) T_(g) (° C.) Prior art Hexply M9 3200 136 3200 854 >70 Epoxy (literature values) Ratio A:B - 1.5:1 1572 53 1860 46 12 37(D) ZnAcAc Ratio A:B - 1.82:1 1584 52 1813 43 5 32 (D) ZnAcAc RatioA:B - 2:1 828 25 1121 22 50 29 (D) ZnAcAc Ratio A:B - 1.75:1 + 1408 524274 43 2 60 (C) desmolux 2738 (D) ZnAcAc Ratio A:B - 1.75:1 + 2546 972920 42 2 — (C) desmolux 2738 (D) TBAA* tetra-n-butyl ammonium acetate

Example 6 Testing of Various Component (D) Catalysts

Samples of dual-cure compositions according to the present inventionwere generated using 2-ethyl hexanol (component A)+Crelan® 403(component B, see Table 1) and several different component (D)catalysts. Each sample was subjected to gel permeation chromatography(GPC) to determine number average molecular weight (M_(n)), weightaverage molecular weight (M_(w)), Z weight average molecular weight(M_(z)) and the polydispersity index (M_(w)/M_(n)) (Table 10). Sampleswhich demonstrate a lower molecular weight or a polydispersity indexbelow 2.0 are indicative of urethane formation rather than allophonateformation leading to crosslinking and are thus not good crosslinkingcatalysts.

TABLE 10 Results of gel permeation chromatography M_(w) M_(z) SampleM_(n) (S.D.) (S.D.) M_(w)/M_(n) Crelan ® 403* 3970 9090 14690 2.29 0%Blank 3920 8580 13930 2.19 1% Zn Acetoacetonate 3950 8760 14630 2.21 1%DBU*** 3160 6360 10550 2.01 0.5% T-12 + 0.5% DBN**** 1940 3360 6040 1.731% DBN 1780 2790 4540 1.57 *see Table 1; **T-12 is dibutyltindilaurate;***DBU is 1,8-diazabicyclo[5.4.0]undec-7-ene; DBN is****1,5-Diazabicyclo(4.3.0)Non-5-Ene

It will be appreciated that the aforementioned embodiments andimplementations are illustrative and various aspects of the inventionmay have applicability beyond the specifically described contexts.Furthermore, it is to be understood that these embodiments andimplementations are not limited to the particular components,methodologies, or protocols described, as these may vary and may be madewithout departing from the spirit and scope of the underlying inventiveconcept. The terminology used in the description is for the purpose ofillustrating the particular versions or embodiments only, and is notintended to limit their scope in the present disclosure which will belimited only by the appended claims.

What is claimed is:
 1. A dual-cure composition containing: (A) amultifunctional polyol; (B) a curing agent containing uretidione groups;(C) a low viscosity unsaturated reactive diluent; (D) at least onereactively activatable catalyst; and (E) a thermal crosslinkinginitiator; wherein the composition cures at 80-130° C.
 2. The dual-curecomposition of claim 1, wherein the heat of polymerization of thedual-cure composition is less than 170 J/g.
 3. The dual-cure compositionof claim 1, wherein the heat of polymerization of the dual-curecomposition is less than 130 J/g.
 4. The dual-cure composition of claim1, further comprising an epoxy functional molecule.
 5. The dual-curecomposition of claim 1, further comprising a free radical scavenger. 6.The dual-cure composition of claim 1, further comprising an antifoamingagent.
 7. The dual-cure composition of claim 1, wherein said component(A) is a free radically reactive monomer selected from the groupconsisting of a vinyl ether, an allyl ether, an acrylate, amethacrylate, a urethane acrylate, allophanate acrylate, epoxy acrylate,alone or in a mixture.
 8. The dual-cure composition of claim 1, whereinsaid component (A) is a non-free radically reactive oligomer selectedfrom the group consisting of an ether, an ester, an epoxy, an alkyd, aurethane, alone or in a mixture.
 9. The dual-cure composition of claim1, wherein said component (B) consists essentially of a curing agentcontaining at least one aliphatic, cycloaliphatic or aromaticpolyisocyanate selected from the group consisting of isophoronediisocyanate (IPDI), hexamethylene diisocyanate (HDI),diisocyanatodicyclohexylmethane (H₁₂MDI), diphenylmethane4,4′-diisocyanate and diphenylmethane 2,4′-diisocyanate (MDI), and 2,4-and 2,6-toluene diisocyanate (TDI),
 10. The dual-cure composition ofclaim 1, wherein said component (C) is a peroxide curable monomerselected from the group consisting of an acrylate, a methacrylate, aurethane acrylate, a urethane methacrylate, a polyester acrylate, apolyester methacrylate, a polyether acrylate, a polyether methacrylate,an allyl ether methacrylate, an allyl ether methacrylate, an esteracrylate, an ester methacrylate, an allophonate urethane methacrylate,an allophonate urethane methacrylate, an epoxy acrylate, an epoxymethacrylate, a vinyl ether, alone or in a mixture.
 11. The dual-curecomposition of claim 1, wherein said component (D) is a lewis acidcomprising at least one metallo-organic catalyst of the general formula:R_(n)MeX_(y) in which Me is a metal, R is an alkyl residue, X is acarboxylate residue, an alcoholate residue, or an acetylacetonateresidue, n=0 or 2, and y=2 or
 3. 12. The dual-cure composition of claim1, wherein said component (D) is Zn acetylacetonate.
 13. The dual-curecomposition of claim 1, wherein said component (E) consists essentiallyof a peroxide or hydro-peroxide compound.
 14. The dual-cure compositionof claim 5, wherein the free radical scavenger is a nitroxide compound.15. A process for the production of a dual-cure composite comprising:(i) homogenizing a pre-polymer composition comprising: (A) amultifunctional polyol; (B) a curing agent containing uretidione groups;(C) a low viscosity unsaturated reactive diluent; (ii) heating thepre-polymer composition to a temperature above the Tg of said component(B); (iii) cooling the heated pre-polymer composition to a temperatureof less than 110° C.; (iv) mixing the cooled pre-polymer compositionwith a dual-cure catalyst composition to form a dual-cure composition,the catalyst composition comprising: (D) at least one reactivelyactivatable catalyst; and (E) a thermal crosslinking initiator; (v)curing the dual-cure composition at a temperature of from 80° C. to 130°C. for a period of time sufficient to form a cured composite.
 16. Theprocess for the production of a dual-cure composite of claim 15, furthercomprising the additional step of: (vi) adding a component (F), which isa fibrous support material to said pre-polymer composition during and/orafter step (i) but before step(v).
 17. The process for the production ofa dual-cure composite of claim 15, wherein the final density of thecured composite is less than 1.15 g/ml.
 18. The process for theproduction of a dual-cure composite of claim 15, wherein the dual-curecomposition has a Tg of from −20° C. to +20° C. and the cured compositehas a Tg of from 70° C. to 130° C.
 19. A prepreg material comprising:(i) at least one fibrous material support, and (ii) a dual-curecomposition comprising: (A) a multifunctional polyol; (B) a curing agentcontaining uretidione groups; (C) a low viscosity unsaturated reactivediluent; (D) at least one reactively activatable catalyst; and (E) athermal crosslinking initiator.
 20. The prepreg material of claim 19,wherein said fibrous material support comprises at least one of carbon,aramid, glass, ceramic, quartz, boron, polyester, polyethylene,polyoxazoline or natural fibers.
 21. The prepreg material of claim 19,wherein the heat of polymerization of the dual-cure composition is lessthan 130 J/g.
 22. The prepreg material of claim 19, wherein the prepregis converted to a composite component by exposure to a temperature offrom 80° C. to 130° C. for a period of time sufficient to form a curedcomposite.